Tipping elements are regional-scale features of the climate that could exhibit threshold-type behaviour in response to human-driven climate change – that is, a small amount of climate change at a critical point could trigger an abrupt and/or irreversible shift in the tipping element. The consequences of such shifts for societies and ecosystems are likely to be severe. Question marks indicate systems whose status as tipping elements is particularly uncertain. There are other potential tipping elements that are missing from the map, for example shallow-water coral reefs (Veron et al. 2009) threatened in part by ocean acidification